The problem I was having with the installer was the Quick install option.. it only installed 3.6, as someone pointed out to me on the Rockbox forum, 3.6 wasn't for the Clip. It was suggested I try installing the 'current build' instead of 'rockbox stable', which I did through the Installation tab instead.
Got it working now, and it's really frickin cool! Definitely a huge improvement over the original UI. I really like the smaller fonts and menu structure, and it seems that skipping tracks is much quicker now too.
I'm gonna have to explore it a bit to see what all of the options are, but it seems very configurable with lots of extra goodies that weren't there before.